Method of and means for the modulation of ultrashort waves



p 19, 1950 H GUTTON- ETAL 2,523,209

METHOD OF AND MEANS FOR THE MODULATION OF ULTRASHORT WAVES Filed July 19. 1946 /N VEN TO/QS HENR/ GUTTON AND I ANTOINE; EAN 0&7'05

Patented Sept. 19, 1950 METHODOF AND' MEANS FOR/THE MODU- LATIONOF ULTRASHORT WAVES Henri Gutton and Antoine Jean Ortusi, Paris, France, assignors to Compagnie Generale De Telegraphic Sans Fil, a corporation of France Application July 19, 1946,'Serial No. 684,819 In France February 6, 1945 Section 1, Public Law 690, August 8, 1946 Patent expires February 6, 1965 '7 Claims.

This inventionis directed to improvements in or relating to methods of and means for the modulation of ultra-short waves in a guide or on a feeder by means of space charge valves such as a magnetron, brake field valve and the like. For the purpose of indicating the underlying principle of the invention the same will be described by way of example as applied to a magnetron.

It will be noted, in the first place, that in. a blocked cylindrical magnetron the electrons which do not reach the anode circulate in the interior of a cylinder the diameter of which is comprised between the diameter of the cathode and that of the anode and there is a very important electronic charge on the surface of this cylinder.

If there be therefore applied, between the cathode and the anode, an electric'field of high frequency, 'the electrons of the spacial charge oscillate radially 'following the frequency of the field. Theory and experience show'that this oscillation is'capabl e "of entering into resonance with a particular frequency depending upon the amount of the magnetic "field H, thepulsation of the resonance'frequenc'y being approximately eH e aa indicating thera-tio of the charge-to the' mass of an electron.

Theory and experience also show-thatin' the vicinity'of the resonance-theapparent capacity of the magnetron varies very rapidly-when"-the pulsation 'w of the field-of high frequencyeva-ries on each side of mo. density -of charge in :a cylindrical-..space :surrounding the cathode isa function of theianode potential; and'the variation of apparent :capacity of the magnetron is itself a function-of the, anode potential, when-the pulsation --w.of the field remains constant.

The invention will be moreparticularly -described with reference to theaccompanying drawings, in which:

Figure 1 illustrates diagrammatically .a device of a transmitter feeding a system radiating through the intermediary of a feeder coupled to a resonator i Fig. 2 re'presents the variations of'the edemcient of transmission of the wave corresponding to' the detuning dof'the resonator;

Fig. 3 illustrates, corresponding to a potential Vofthe'ano'de, 'va'riati'on curves of the transmission coe'fiicienfi'for different "values of the magnetic field;

On the other hand,- -.the

of the resonator and in nator -r to the transmission frequency and suitably selecting its excess potential on"-load,'there may be obtained the almost total reflection of 'the incident wave. The curve representing the coeflicient of transmission of the wave'as a function of the detuning d of the resonator therefore assumes the form illustrated in"Fig. 2. It shows all the more pointedly that "the looser the'coupling of'the resonator to the feeder, 'so-the coefficient of transmission may pass from a value very close to 1, at A, to a value very close'to '0, at B, and'this all themore suddenly the greater the modification of the capacity C of the resonator about the resonance.

With such a resonator r, it has been possible to obtain experimentally the group of curves shown in Fig. 3. There is shown in abscissae the anodic potential V applied to the magnetron ordinates, the coefiicient of transmission T of the resonator. Each curve of the group corresponds to a value of the magnetic field H, expressed in gausses, a value'close to that of the 'magnetic field causing the'res'o nance. The value if of the transmission coeffioient corresponds to the case where no potential is applied to the anode. There will" rererably be chosen a mean potential v corresponding to a mean point M located on a characteristic ab and the modulation will be obtained by applying to the anode of the magnetron a variable potential the amplitude of maximum variation of which will be equal to av= bi1. As will be seen from Fig. 3, the preceding group comprises curves that are almost linear, thus permitting very important ratesof modulation of the order of Without appreciable distortion to be obtained. v

On the other hand, the modulator magnetron may be of comparatively small capacity, so that its impedance remaining large athigh frequencies of modulation, it permits, without appre ciable attenuation, the-modulation of, for example, very rapid television signals.

Finally, a particularly important advantage of the system according to the present invention is that the magnetron modulates the transmitter without absorbing energy. The characteristics of Fig. 3 have, in fact, all been drawn for potentials very much below the potential necessary to unblock the valve and practically the anode current never exceeds 1 milliarnpere.

It is thus for example that for a magnetron which had a cathode of a diameter of 4 mm. and an anode of mm. it has been found that to modulate a wave of cm. it was necessary to use a magnetic field approximating to 500 gauss and an anode potential of 250 volts, the amplitude of the potential of modulation being equal to 125 volts to obtain a total modulation. In this case, the energy necessary for the modulation obtained with a pentode of low reception frequency, was of the order of only 0.5 watt.

But about half the mean energy conveyed by the incident wave is returned to the transmitter; the result is a modification of the charge of the generator. To avoid this, the invention provides a double modulator the principle of which is as follows:

The transmitter is charged on two feeders, or two electromagnetic guides, in such manner that each of these transmits half the energy. Symmetrically there are coupled two resonators on each of these guides. The capacities of these resonators each comprise a magnetron the anode potential of which is modulated. The first magnetron receives the modulated potential to be transmitted and the second a complementary potential in such manner that the sum of these two potentials remains constant. Under these conditions, the transmitter supports a constant charge.

The methods which permit these two complementary modulations to be obtained are, furthermore, numerous; for example, a transformer the secondary of which has a central point earthed, may be used for the transmission of telephonic signals; or, again, an amplification may be made in push-pull, etc.

When it is a matter of sinusoidal signals or of telephonic signals, one or other of the complementary modulations may be transmitted indifferently to the radiator; if it is a question, on the contrary, of the transmission of television signals, only the wave correctly modulated can be used to transmit to the aerial. The complementary modulated wave is eliminated by terminating the guide which transmits it by its characteristic impedance; this can be effected either by a radiator fitted to the extremity of the guide, which radiator radiates the energy. in a direction other than that of the receiver, or by a resistance fitted at the extremity of the guide.

For certain problems of radio guidance two complementary modulations transmitted by two dififerent aer-ials, the diagrams of radiation of which intersect each other, are frequently used. In such systems it is very advantageous to employ this method of modulation, for the complementary modulations can be very rapid since there is no mechanical permutation at all.

It has been pointed out at the commencement that this method of modulation may be utilized with other kinds of valves, in which the capacity in high frequency between two electrodes undergoes variations when the potential of one of the electrodes varies as compared with the other. In particular, the magnetron can be replaced by a valve with brake field; there exists, as a matter of fact, in this valve, as in the magnetron, a space charge capable of resonating at a definite frequency; the eiTect produced by causing the potential of the retarding plate or that of the accelerating grid to vary, is similar to that observed with the magnetron.

Naturally, it is impossible to describe all the forms of carrying the invention into effect. By way of a non-restrictive example, one of these will be described.

The transmitter E (Fig. 4), for example, a velocity modulation valve, is coupled to a guide G of rectangular section which can only transmit the wave H01 on the frequency of the transmitter. Coupling takes place by a radiating aerial in the interior of a guide element closed on one side by a piston P, and on the other side by a suitable slot F. The whole is fitted in such manner that the transmitter is charged under the desired conditions.

The preceding guide is separated into two guides I and 2, by the interposing of a metallic partition Q. Arrangements are made so that there should be no reflection on the incident wave on this discontinuity. This may be accomplished by annulling the reflection by a suitable adaptor D. Half the incident energy then circulates in each of the guides l and 2.

This being so, the energies transmitted by guides I and 2 will be modulated complementarily by using two concentric lines L1 and L2 arranged symmetrically and the central' conductors of which are placed in communication with the metallic wall Q through a flat condenser S. At the other extremities of the concentric lines there are connected two identical magnetrons M1 and M2 the anodes a1 and a2 of which are respectively connected to the central conductors of L1 and of L2, and the cathodes ,81, {32 of which are respectively in connection with the external parts of L1 and L2. In Fig. 4, there are shown furthermore at 1, 1.2 the magnets of the magnetrons, and by 71, 2, their respective heating circuits. As regards Fig. 5, it gives the details of the connections of each of the magnetrons M1 or M2.

On the other hand, the anode potentials of the two magnetrons Mrand M2 on which are superposed the modulation potentials, are produced by means of two conducting wires f1, f2 (Fig. 6) arranged normally to the elastic field q and connected respectively to the two electrodes of the condenser S; these wires f1 and f2 emerge furthermore from the guide through an insulator.

Fig. 6 represents a section of Fig. 4, which section is made perpendicularly to the plane of the latter, at the level of the condenser S.

Finally, the branch l of the guide (Fig. 4) which has received the modulation suitable to be transmitted, is terminated by the radiator K, which is an electromagnetic horn adapted by a suitable corrector D1; whilst the branch 2 which receives the complementary modulation from I, is terminated by a resistance R adjusted by means of a slot F1 and a piston P1 suitably actuated.

According to this example of the embodiment of this invention, there can be seen the principal advantages of the modulation of. the ultrashort waves. 1

1. The transmitter not being modulated, its stability of frequency remains very high, and its point of operation can be chosen under the best conditions; in general it will therefore be useless to pilot it.

2. The modulation may be very rapid, since it is only limited in the direction of high frequencies by the capacity of the electrodes of the modulatorpit will thus be possible for example to pass television signals. However, the transmitter not being modulated, the modulation band will not have to pass into the circuits of the high frequency generator which consequently may preserve great supertension favorable to output and to the stability of the generator wave.

3. The energy necessary for modulating-powers which may be of several hundreds of watts, remains very slight, of the order of a watt, for this energy is only used to modify the capacity of the valve by displacement of the space charged.

4. The modulator does not absorb the energy coming from the transmitter; it can thus be of small dimensions and consequently of very low cost price.

5. The energy furnished by a single generator can be delivered into a large number of feeders or of guides, and modulate in a totally independent manner on each of these guides. This may be utilized to produce a multiplex having a large number of paths.

What we claim as our invention and desire to secure by Letters Patent of the United States is:

1. A system for the modulation of an ultrahigh frequency Wave, comprising a generator of the said wave, a transmission guide for said Wave, a transmission line connected laterally to the said guide, a magnetron including an anode and cathode, connections between said magnetron and said line, the characteristics of the said line and of the said magnetron being chosen in such a way that their aggregate resounds on the frequency of the said wave, means connected with the said magnetron for varying the direct voltage between the anode and cathode of the said ma netron means for applying a continuous potential beween the anode and the cathode of said magnetron, regulated in such a way that the latter is in the blocked state, and means for applying a variable potential in series with the said con tinuous potential, said variable potential being regulated in such a way as to maintain the tube in the blocked state.

2. A system for the modulation of an ultrahigh frequency wave, comprising a generator of the said wave, a transmission guide for said wave, a transmission line connected laterally to the said guide, a magnetron comprising a cathode, an anode concentric with the cathode, and a magnetic field directed along the common axis of the said anode and of the said cathode, means for varying the voltage between the anode and the cathode of the said magnetron, means connected with the said magnetron for giving to the said magnetic field a value slightly different from the value which determines the electronic resonance of the space charge of the magnetron on the frequency of the wave to be modulated, means for applying a continuous potential between the anode and the cathode of said magnetron, regulated in such a Way that the latter is in the blocked state, and means for applying a variable potential in series with the said continuous potential, said variable potential being regulated in such a way as to maintain the tube in the blocked state.

3. A system for the modulation of an ultrahigh frequency wave, comprising a generator of the said wave, a transmission guide for said wave, a conductive wall separating the said guide into twoother guides, a transmission line, connected laterally to one of said two guides, a magnetron connected with the said line, and comprising a cathode, an anode concentric with the cathode, and a magnetic field directed alongthe common axis of the said anode and of the said cathode, another transmission line connected laterally to the second guide, another magnetron connected with the said lin and comprising a cathode, an anode concentric with the cathode, and a magnetic field directed along the common axis of the said anode and of the said cathode, means connected with the said magnetrons for giving to the said magnetic fields values slightly different from the values which determine the electronic resonance of the space charges of the magnetrons on the frequency of the waves to be modulated, and means connected with the said magnetrons for applying between their electrodes modulation voltages equal in amplitude and opposite in phase.

4. A system as set forth in claim 3, wherein the modulator magnetrons are identical and are of the cylindrical type with full anode.

5. A system for the modulation of an ultrahigh frequency wave comprising a generator of the said wave, a transmission guide for said wave, a transmission line connected laterally to the said guide, a magnetron including an anode and cathode, connections between said magnetron and said line, the characteristics of the said line and of the said magnetron being chosen in such a way that they conjointly resonate at the frequency of said wave, means for applying a continuous potential between the anode and the cathode of said magnetron regulated in such a way that the latter is in the blocked state, means for applying a variable potential in series with the said continuous potential, said variable potential being regulated in such a way as to main tain the tube in the blocked state, means for establishing a magnetic field parallel to the cathode and means for regulating said field in such a way that it is slightly different from the field determining the electronic resonance of the space charge on the wave to be modulated.

6. A system for the amplitude modulation of an ultra-high frequency wave, comprising in combination a generator for supplying an ultrahigh frequency wave, a transmission guide for said wave, a circuit tunable to this wave composed of a transmission line coupled laterally to the said guide and a magnetron including a cathode, an anode concentric with the cathode, and a magnetic field directed along the common axis of the said anode and the said cathode, means for applying a continuous potential between the anode and the cathode of said magnetron, regulated in such a way that the latter is in the blocked state, means for applying a variable potential in series with the said continuous potential, said variable potential being regulated in such a way as to maintain the tube in the blocked state, and means for regulating said magnetic field in such a way that it is slightly different from the field determining the electronic resonance of the space charge on the wave to be modulated.

7. In a system for amplitude modulation of an ultra-high frequency wave circulating in a transmission channel such as a guide, a circuit tunable to the said wave coupled laterally with said guide, a magnetron in this circuit comprising a cathode and an anode surrounding it, means for introducing a magnetic field between said cathode 7 and anode, means for energizing-the said mag,- REFERENCES CITED matron an of said means being adjusted so as to The following references are of-reco r d in the maintain the magnetron in a, blocked state, me of this patent; means for applying the modulating voltage between said anode and cathode the amplitude of 5 UNITED STATES PATENTS which is adjusted so as to maintain the mag- Number Name Date netron in said blocked condition, the said mag- 2,106,770 Southworth et a1. Feb. 1, 1938 netic field being given an intensity slightly dif- 2,121,737 Hansell June 21, 1938 ferent from that determining the electronic reso- 2,196,392 Hansell Apr. 9, 1940 nance of the space charge to the wave to be 10 2,211,003 Conklin Aug. 13, 1940 modulated. 2,223,058 Christ Nov. 26, 1940 HENRI GUTTON. 2,293,945 Pawsey et a1 Aug. 25, 1942 ANTOINE JEAN ORTUSI. 2,393,414 Roberts Jan. 22, 1946 

